Effects of Nb and Mo on 1200 °C Steam Oxidation and Mechanical Properties of FeCrAl Alloys for Fuel Cladding Materials

Iron–chromium–aluminium (FeCrAl) alloy compositions should be optimised to improve performance. The effects of Nb and Mo on the high-temperature steam oxidation of FeCrAl alloys were investigated at 1200 °C. The oxide film of a series of alloys with different Nb contents mainly comprised Al2O3 and the surface morphology was wrinkled. For the series alloys with different Mo contents, when Mo was greater than 2 wt.%, the oxide film component also contained MoO3, in addition to Al2O3, with the presence of micropores. The oxidation weight gain decreased with Nb, owing to a great many Laves phases, which impeded the outward diffusion of Al. The oxidation weight gain increased with Mo, and this was attributed to the volatilisation of MoO3, which promoted the diffusion of oxygen. The yield strength of FeCrAl alloys increased with increased Nb and Mo and decreased with oxidation time. Nb and Mo promoted the precipitation of the Laves phases and increased the hindrance to grain boundaries, which favoured fine grain strengthening. This was critical to obtaining FeCrAl fuel cladding alloys with great steam oxidation resistance and mechanical properties.